The disclosure of Japanese Patent Application No. 2001-89803 filed on Mar. 27, 2001, including the specification, drawings and abstract are incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an oil pump used in an internal combustion engine for a vehicle and a method for operating the oil pump.
2. Description of Related Art
Generally a trochoid pump is well known as being employed for lubricating an internal combustion engine (hereinafter simply referred to as an engine) for a vehicle as disclosed in, for example, JP-A-10-77817. The aforementioned trochoid pump has a shaft that is rotated by a driving force of a crankshaft of the engine so as to discharge the oil by quantity proportional to a revolution speed of the engine and to generate a hydraulic pressure. When a discharge pressure of the pump is detected to become equal to or greater than a predetermined pressure value, a relief valve disposed on the discharge port of the pump opens to communicate the discharge port and an intake port. As a result, a portion of the oil discharged from the discharge port is returned to the intake port. This makes it possible to prevent a damage of or oil leakage from an engine lubricating system.
In the above-described oil pump for the engine, a surplus of the oil is returned to a low-pressure side of the lubricating system through a relief valve, thus preventing the damage and oil leakage occurred in the engine lubricating system. The aforementioned mechanism, however, may cause a loss of a mechanical energy that forces a valve element against a biasing force generated by a spring of the relief valve, and a loss of a driving energy that circulates the oil by returning the surplus of the oil pumped up by the oil pump to the low-pressure side of the system. This may reduce a fuel consumption efficiency, resulting in vibration or noise in the engine.
The hydraulic pressure and the oil discharge quantity controlled to required values at a high engine speed may not meet the required hydraulic pressure and the oil discharge quantity at a low speed of the engine, resulting in insufficient hydraulic pressure value and insufficient quantity of the oil. Especially when the vehicle is in an idling state at a high temperature of the engine, the hydraulic pressure of the engine is minimized. Therefore, the hydraulic pressure value and the oil quantity supplied to a bearing, valve system, and other oil lubricating system may become insufficient.
An object of the invention is to provide an oil pump for an engine and a method of operating the oil pump, which prevents the hydraulic pressure value or an oil discharging quantity from being excessively generated at a middle or a high revolution speed of the engine, and improves driveability and reliability of the engine at a low revolution speed.
Another object of the invention is to provide an oil pump for an engine and a method for operating the oil pump, in which a basic oil discharging pressure is generated by a power pump driven by the driving force of the engine, while controlling the basic oil discharging force using an electric signal.
Another object of the invention is to provide an oil pump for an engine and a method for operating the oil pump, in which a power pump serving as a main pump driven by the driving force generated by the engine and an electric pump serving as an auxiliary pump operated by an electric signal are combined to constitute the oil pump.
In the oil pump according to the invention, a power pump rotated together with the driving shaft of the engine and the electric pump rotated by the electric motor are provided in the same pump housing. This makes it possible to cause any of the pumps to compensate the other that is damaged. This also makes it possible to enhance the power of the oil pump by operating both pumps. The oil pump of the invention can be operated in various ways in accordance with the intended use by controlling distribution of the driving force supplied from two types of driving sources. The basic oil discharging pressure supplied from the power pump can be adjusted or corrected by the discharging pressure generated by the electric pump. As a result, the oil pump can be operated with high efficiency by executing appropriate energy distribution.
As the driving shaft of the engine is generally used as the driving source of the power pump, the resultant discharging pressure and the discharging quantity are adapted to the engine speed. Employment of the electric pump as an auxiliary pump in addition to the power pump as the main pump allows a precision control of the engine that is well adapted to a running state of the engine or the intention of a vehicle operator.
The electric pump serving as the auxiliary pump allows reduction of maximum capacity of the power pump serving as the main pump. Therefore, the electric pump is operated in the vehicle speed range where the oil discharging pressure generated by the power pump becomes insufficient so as to increase the oil discharging pressure and the oil discharging quantity to appropriate values. In the middle speed or high speed range where the oil discharging pressure becomes excessive, the oil discharging pressure or the oil discharging quantity is controlled to a minimum value. While in the low vehicle speed range, sufficient oil discharging pressure or oil discharging quantity can be achieved.
An oil pump for an internal combustion engine according to the invention includes a check valve that is disposed in an oil passage for connecting a discharge port of the power pump to a discharge port of the electric pump such that an oil is allowed to flow only in a direction from the electric pump to the power pump. As the above-described oil pump allows the power pump to be operated alone within the pump housing, the oil pump of the invention is useful as being a combined pump unit including accessories of the oil pump.
In a method of operating the aforementioned oil pump of the invention, a drive circuit for driving the electric pump is actuated when the engine is operated for at least a predetermined period of time, and oil temperature reaches at least about 80xc2x0 C. As a result, the electric pump is operated forcibly when a period for operating the engine continues for a long period of time, or oil temperature is high. As a result, the oil pump may be prevented from being in a stuck state owing to sludge contained in the oil, thus protecting functions of the oil pump.
In a method of operating the aforementioned oil pump of the invention, the electric pump is operated for a predetermined time period after turning off an ignition switch of the engine. The electric pump is preliminarily operated such that the next re-start of the engine can be smoothly operated.